1. Field of the Invention
The present invention relates to a recording apparatus, and more particularly, to a magnetic field modulation magnet-optical recording apparatus recording information digitally by modulating a magnetic field to be applied to a magnet-optical recording medium according to the information to be recorded utilizing thermo-magnetic effect.
2. Description of the Background Art
FIG. 13 shows the structure of a recording system of a conventional magnet-optical recording apparatus.
Referring to FIG. 13, light provided from a laser light source 5 by a laser driving circuit 7 is modulated to locally irradiate via a condenser lens 9 a magnetic thin film 13 formed on the surface of a magnet-optical recording medium 1 such as a magnet-optical disc driven rotatably by a motor 3. The portion of the recording medium on which light is directed has the magnet holding force reduced due to the thermal energy caused by the irradiation. By establishing a flow of a predetermined current to a magnetic head coil 106 under this condition, a weak external magnetic field is applied to reverse magnetization only in the light irradiated region to carry out recording of the information.
The reading out method of the recorded information (residual magnetization) takes advantage of the inversion of the plane of polarization of a reflecting light or a transmitting light with respect to the direction of magnetization when a linear polarized light is directed to a magnetic body.
Known technology relating to the present application is listed as follows.
(1) Japanese Patent Laying-Open No. 56-44285
An optical recording/reproduction device is disclosed that modulates the intensity of a laser light by an FM video signal and a FM audio signal to carry out FM recording.
(2) Japanese Patent Laying-Open No. 3-12006
A method of generating a high-frequency field of a high level in a magnetic head coil is disclosed in a magnet-optical recording method by a magnetic field modulation system.
(3) Japanese Patent Laying-Open No. 64-55762
A bias magnetic field generating apparatus is disclosed for changing the driving current of a magnetic head coil. A magnetic field of a constant intensity can be applied to the recording medium even when the distance between the magnetic head coil and the recording medium changes by virtue of the amplitude of the driving current of the magnetic head coil being controlled by a focus error signal.
(4) Japanese Patent Laying-Open No. 63-244402
In a magnet-optical recording apparatus of a magnetic modulating system, a magnetic head driving circuit is disclosed that has a sudden rising and falling edge of a driving current of the magnetic head coil.
In principle, it is possible to FM record an information signal on a magnet-optical recording medium in a magnet-optical recording apparatus of a magnetic field modulation system by combining the known art of the above listed (1) and (2). More specifically, the magnetic head driving current which is FM modulated by the output signal of the FM modulator used in the apparatus of (1) can be applied to the magnetic head coil disclosed in (2).
However the above combination of the prior arts of (1) and (2) requires an FM modulator and also a driving circuit for conducting the driving current flow to the magnetic head coil, resulting in a problem that simplification and miniaturization of the configuration of a magnet-optical recording apparatus is prevented. It is to be noted that the method of (2) has a direct current magnetic field applied overlying the modulation magnetic field. The object thereof is to stabilize magnetization in the not-yet recorded portion, and has no meaning in carrying out FM recording.
The bias magnetic field generating apparatus of the above (3) for maintaining at a constant level the intensity of the direct current bias magnetic field applied to a recording medium is used in a magnet-optical recording apparatus of a photomodulation system. There is no disclosure of an arrangement for carrying out FM recording by a magnetic field modulation system in (3). There is also no disclosure of an arrangement for carrying out FM recording in (4).